An air cleaner is a part for filtering air containing dust and supplying filtered clean air to an engine. For the purpose of maintenance, a filter for filtering air is detachably attached to a casing forming a body of the air cleaner. When the filter is attached to the casing with a gap left between the filter and the casing, air containing dust is likely to enter through the gap into a carburetor on an engine side. To this end, JP-A-10-252585, for example, proposes an air cleaner with a sealing frame of an elastic material interposed between a casing and a filter, leaving no gap therebetween. The proposed air cleaner arrangement will now be described with reference to FIG. 6 hereof.
As shown in FIG. 6, the conventional air cleaner 100 is comprised of a casing 102 with a communication hole (101) communicating with a carburetor, not shown, a sealing frame 103 made of a elastic material and fitted in the casing 102, a filter 104 engaged with the sealing frame 103, a backup frame 105 for supporting the filter 104, and a cover 106 for securing the backup frame 105. The backup frame 105 presses the sealing frame 103 against the casing 102 to thereby prevent dust from passing between the sealing frame 103 and the casing 102.
However, the conventional air cleaner has a drawback in that the casing 102 is likely to have dimension errors that lead to distortion in a bearing surface 108 of the sealing frame 103. Similarly, the backup frame 105 and the cover 106 are likely to have dimension errors that result in a shortage in the pressing force of the backup frame 105 against the sealing frame 103. Such distortion and pressing force shortage will give rise to a gap 107 between the casing 102 and the sealing frame 103, thus deteriorating a sealing effect between them. Consequently, there is a demand for an improvement in a sealing effect between the sealing frame and the casing.